add a way to tell synapse to recover a room, after a database disaster #8487
Description
This issue has been migrated from #8487.
matrix-org/synapse#6176 added the server-side support necessary so that a homeserver can just send a /state request over federation to get back everything it needs to recover a room after losing all of its data on a room. I'm not sure what, if anything, happened on the client side though.